A rotary electric machine basically comprises a casing, a stator rigidly connected to the casing, a rotor, for example of the type with permanent magnets, enclosed by the casing and rotatably connected to the latter.
When the electric machine functions as a motor, the rotor is rotationally driven by powering the stator through an electronic circuit or control circuitry, which in this case, is also positioned inside the casing.
The casing is then closed by a cover with a terminal strip on the outside of it to power the electronic circuitry and, hence, the electric motor. The electronic drive circuitry, which is mounted on a respective plate, is interposed between the stator and the cover.
The control circuitry comprises a power circuit and must therefore be provided with a heat sink for absorbing the heat produced by the electronic power components during operation.
At the same time, the assembly must guarantee an efficient electrical connection between the electronic circuit and the electric motor so as to ensure that the motor operates correctly.
In the case of electric motors with built-in electronic circuitry, absorption of excess heat is not easy to achieve because it is difficult to make an effective electrical connection between the electronic circuitry and the motor and good thermal contact between the electronic circuitry and a corresponding heat sink, in particular the cover.
The main problems are due precisely to the fact that, because the casing has to be closed with the cover, it is difficult, with the motor substantially closed, to make all the electrical and mechanical connections in optimum manner.
To enable the assembly to be closed, prior art solutions provide at least one sliding contact, such as a connector, for example, which is easily subject to problems of reliability and efficiency for example on account of vibrations, contact wear, or operating temperature, between the motor and the electronic circuitry or between the electronic circuitry and the terminal strip.
In the first case, the electronic circuitry is rigidly connected to the cover in order to optimize heat exchange with the latter and, when the casing is closed, a sliding contact connects the electronic circuitry to the motor. In this case, therefore, the heat sink function takes priority over the reliability of the connection between the electronic circuitry and the motor.
In the second case, the electronic circuitry is effectively and rigidly connected to the motor, for example by soldering, whilst the contact of the circuitry with the cover is not particularly effective in terms of heat exchange on account of the necessary closing tolerances.
Thus, in the latter solution, the electronic circuitry is not effectively pressed against the heat sink, for example on account of assembly tolerances. Also, as already mentioned, there is normally a sliding contact, with all its inherent limitations, between the electronic circuitry and the terminal strip on the outside.